1426 lines · cpp
1//===--- CGVTables.cpp - Emit LLVM Code for C++ vtables -------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// This contains code dealing with C++ code generation of virtual tables.10//11//===----------------------------------------------------------------------===//12 13#include "CGCXXABI.h"14#include "CGDebugInfo.h"15#include "CodeGenFunction.h"16#include "CodeGenModule.h"17#include "clang/AST/Attr.h"18#include "clang/AST/CXXInheritance.h"19#include "clang/AST/RecordLayout.h"20#include "clang/Basic/CodeGenOptions.h"21#include "clang/CodeGen/CGFunctionInfo.h"22#include "clang/CodeGen/ConstantInitBuilder.h"23#include "llvm/IR/IntrinsicInst.h"24#include "llvm/Transforms/Utils/Cloning.h"25#include <algorithm>26#include <cstdio>27#include <utility>28 29using namespace clang;30using namespace CodeGen;31 32CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)33 : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}34 35llvm::Constant *CodeGenModule::GetAddrOfThunk(StringRef Name, llvm::Type *FnTy,36 GlobalDecl GD) {37 return GetOrCreateLLVMFunction(Name, FnTy, GD, /*ForVTable=*/true,38 /*DontDefer=*/true, /*IsThunk=*/true);39}40 41static void setThunkProperties(CodeGenModule &CGM, const ThunkInfo &Thunk,42 llvm::Function *ThunkFn, bool ForVTable,43 GlobalDecl GD) {44 CGM.setFunctionLinkage(GD, ThunkFn);45 CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,46 !Thunk.Return.isEmpty());47 48 // Set the right visibility.49 CGM.setGVProperties(ThunkFn, GD);50 51 if (!CGM.getCXXABI().exportThunk()) {52 ThunkFn->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);53 ThunkFn->setDSOLocal(true);54 }55 56 if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())57 ThunkFn->setComdat(CGM.getModule().getOrInsertComdat(ThunkFn->getName()));58}59 60#ifndef NDEBUG61static bool similar(const ABIArgInfo &infoL, CanQualType typeL,62 const ABIArgInfo &infoR, CanQualType typeR) {63 return (infoL.getKind() == infoR.getKind() &&64 (typeL == typeR ||65 (isa<PointerType>(typeL) && isa<PointerType>(typeR)) ||66 (isa<ReferenceType>(typeL) && isa<ReferenceType>(typeR))));67}68#endif69 70static RValue PerformReturnAdjustment(CodeGenFunction &CGF,71 QualType ResultType, RValue RV,72 const ThunkInfo &Thunk) {73 // Emit the return adjustment.74 bool NullCheckValue = !ResultType->isReferenceType();75 76 llvm::BasicBlock *AdjustNull = nullptr;77 llvm::BasicBlock *AdjustNotNull = nullptr;78 llvm::BasicBlock *AdjustEnd = nullptr;79 80 llvm::Value *ReturnValue = RV.getScalarVal();81 82 if (NullCheckValue) {83 AdjustNull = CGF.createBasicBlock("adjust.null");84 AdjustNotNull = CGF.createBasicBlock("adjust.notnull");85 AdjustEnd = CGF.createBasicBlock("adjust.end");86 87 llvm::Value *IsNull = CGF.Builder.CreateIsNull(ReturnValue);88 CGF.Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);89 CGF.EmitBlock(AdjustNotNull);90 }91 92 auto ClassDecl = ResultType->getPointeeType()->getAsCXXRecordDecl();93 auto ClassAlign = CGF.CGM.getClassPointerAlignment(ClassDecl);94 ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(95 CGF,96 Address(ReturnValue, CGF.ConvertTypeForMem(ResultType->getPointeeType()),97 ClassAlign),98 ClassDecl, Thunk.Return);99 100 if (NullCheckValue) {101 CGF.Builder.CreateBr(AdjustEnd);102 CGF.EmitBlock(AdjustNull);103 CGF.Builder.CreateBr(AdjustEnd);104 CGF.EmitBlock(AdjustEnd);105 106 llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);107 PHI->addIncoming(ReturnValue, AdjustNotNull);108 PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),109 AdjustNull);110 ReturnValue = PHI;111 }112 113 return RValue::get(ReturnValue);114}115 116/// This function clones a function's DISubprogram node and enters it into117/// a value map with the intent that the map can be utilized by the cloner118/// to short-circuit Metadata node mapping.119/// Furthermore, the function resolves any DILocalVariable nodes referenced120/// by dbg.value intrinsics so they can be properly mapped during cloning.121static void resolveTopLevelMetadata(llvm::Function *Fn,122 llvm::ValueToValueMapTy &VMap) {123 // Clone the DISubprogram node and put it into the Value map.124 auto *DIS = Fn->getSubprogram();125 if (!DIS)126 return;127 auto *NewDIS = llvm::MDNode::replaceWithDistinct(DIS->clone());128 // As DISubprogram remapping is avoided, clear retained nodes list of129 // cloned DISubprogram from retained nodes local to original DISubprogram.130 // FIXME: Thunk function signature is produced wrong in DWARF, as retained131 // nodes are not remapped.132 NewDIS->replaceRetainedNodes(llvm::MDTuple::get(Fn->getContext(), {}));133 VMap.MD()[DIS].reset(NewDIS);134 135 // Find all llvm.dbg.declare intrinsics and resolve the DILocalVariable nodes136 // they are referencing.137 for (auto &BB : *Fn) {138 for (auto &I : BB) {139 for (llvm::DbgVariableRecord &DVR :140 llvm::filterDbgVars(I.getDbgRecordRange())) {141 auto *DILocal = DVR.getVariable();142 if (!DILocal->isResolved())143 DILocal->resolve();144 }145 if (auto *DII = dyn_cast<llvm::DbgVariableIntrinsic>(&I)) {146 auto *DILocal = DII->getVariable();147 if (!DILocal->isResolved())148 DILocal->resolve();149 }150 }151 }152}153 154// This function does roughly the same thing as GenerateThunk, but in a155// very different way, so that va_start and va_end work correctly.156// FIXME: This function assumes "this" is the first non-sret LLVM argument of157// a function, and that there is an alloca built in the entry block158// for all accesses to "this".159// FIXME: This function assumes there is only one "ret" statement per function.160// FIXME: Cloning isn't correct in the presence of indirect goto!161// FIXME: This implementation of thunks bloats codesize by duplicating the162// function definition. There are alternatives:163// 1. Add some sort of stub support to LLVM for cases where we can164// do a this adjustment, then a sibcall.165// 2. We could transform the definition to take a va_list instead of an166// actual variable argument list, then have the thunks (including a167// no-op thunk for the regular definition) call va_start/va_end.168// There's a bit of per-call overhead for this solution, but it's169// better for codesize if the definition is long.170llvm::Function *171CodeGenFunction::GenerateVarArgsThunk(llvm::Function *Fn,172 const CGFunctionInfo &FnInfo,173 GlobalDecl GD, const ThunkInfo &Thunk) {174 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());175 const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();176 QualType ResultType = FPT->getReturnType();177 178 // Get the original function179 assert(FnInfo.isVariadic());180 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);181 llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);182 llvm::Function *BaseFn = cast<llvm::Function>(Callee);183 184 // Cloning can't work if we don't have a definition. The Microsoft ABI may185 // require thunks when a definition is not available. Emit an error in these186 // cases.187 if (!MD->isDefined()) {188 CGM.ErrorUnsupported(MD, "return-adjusting thunk with variadic arguments");189 return Fn;190 }191 assert(!BaseFn->isDeclaration() && "cannot clone undefined variadic method");192 193 // Clone to thunk.194 llvm::ValueToValueMapTy VMap;195 196 // We are cloning a function while some Metadata nodes are still unresolved.197 // Ensure that the value mapper does not encounter any of them.198 resolveTopLevelMetadata(BaseFn, VMap);199 llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap);200 Fn->replaceAllUsesWith(NewFn);201 NewFn->takeName(Fn);202 Fn->eraseFromParent();203 Fn = NewFn;204 205 // "Initialize" CGF (minimally).206 CurFn = Fn;207 208 // Get the "this" value209 llvm::Function::arg_iterator AI = Fn->arg_begin();210 if (CGM.ReturnTypeUsesSRet(FnInfo))211 ++AI;212 213 // Find the first store of "this", which will be to the alloca associated214 // with "this".215 Address ThisPtr = makeNaturalAddressForPointer(216 &*AI, MD->getFunctionObjectParameterType(),217 CGM.getClassPointerAlignment(MD->getParent()));218 llvm::BasicBlock *EntryBB = &Fn->front();219 llvm::BasicBlock::iterator ThisStore =220 llvm::find_if(*EntryBB, [&](llvm::Instruction &I) {221 return isa<llvm::StoreInst>(I) && I.getOperand(0) == &*AI;222 });223 assert(ThisStore != EntryBB->end() &&224 "Store of this should be in entry block?");225 // Adjust "this", if necessary.226 Builder.SetInsertPoint(&*ThisStore);227 228 const CXXRecordDecl *ThisValueClass = Thunk.ThisType->getPointeeCXXRecordDecl();229 llvm::Value *AdjustedThisPtr = CGM.getCXXABI().performThisAdjustment(230 *this, ThisPtr, ThisValueClass, Thunk);231 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr,232 ThisStore->getOperand(0)->getType());233 ThisStore->setOperand(0, AdjustedThisPtr);234 235 if (!Thunk.Return.isEmpty()) {236 // Fix up the returned value, if necessary.237 for (llvm::BasicBlock &BB : *Fn) {238 llvm::Instruction *T = BB.getTerminator();239 if (isa<llvm::ReturnInst>(T)) {240 RValue RV = RValue::get(T->getOperand(0));241 T->eraseFromParent();242 Builder.SetInsertPoint(&BB);243 RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);244 Builder.CreateRet(RV.getScalarVal());245 break;246 }247 }248 }249 250 return Fn;251}252 253void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,254 const CGFunctionInfo &FnInfo,255 bool IsUnprototyped) {256 assert(!CurGD.getDecl() && "CurGD was already set!");257 CurGD = GD;258 CurFuncIsThunk = true;259 260 // Build FunctionArgs.261 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());262 QualType ThisType = MD->getThisType();263 QualType ResultType;264 if (IsUnprototyped)265 ResultType = CGM.getContext().VoidTy;266 else if (CGM.getCXXABI().HasThisReturn(GD))267 ResultType = ThisType;268 else if (CGM.getCXXABI().hasMostDerivedReturn(GD))269 ResultType = CGM.getContext().VoidPtrTy;270 else271 ResultType = MD->getType()->castAs<FunctionProtoType>()->getReturnType();272 FunctionArgList FunctionArgs;273 274 // Create the implicit 'this' parameter declaration.275 CGM.getCXXABI().buildThisParam(*this, FunctionArgs);276 277 // Add the rest of the parameters, if we have a prototype to work with.278 if (!IsUnprototyped) {279 FunctionArgs.append(MD->param_begin(), MD->param_end());280 281 if (isa<CXXDestructorDecl>(MD))282 CGM.getCXXABI().addImplicitStructorParams(*this, ResultType,283 FunctionArgs);284 }285 286 // Start defining the function.287 auto NL = ApplyDebugLocation::CreateEmpty(*this);288 StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,289 MD->getLocation());290 // Create a scope with an artificial location for the body of this function.291 auto AL = ApplyDebugLocation::CreateArtificial(*this);292 293 // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.294 CGM.getCXXABI().EmitInstanceFunctionProlog(*this);295 CXXThisValue = CXXABIThisValue;296 CurCodeDecl = MD;297 CurFuncDecl = MD;298}299 300void CodeGenFunction::FinishThunk() {301 // Clear these to restore the invariants expected by302 // StartFunction/FinishFunction.303 CurCodeDecl = nullptr;304 CurFuncDecl = nullptr;305 306 FinishFunction();307}308 309void CodeGenFunction::EmitCallAndReturnForThunk(llvm::FunctionCallee Callee,310 const ThunkInfo *Thunk,311 bool IsUnprototyped) {312 assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&313 "Please use a new CGF for this thunk");314 const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurGD.getDecl());315 316 // Adjust the 'this' pointer if necessary317 const CXXRecordDecl *ThisValueClass =318 MD->getThisType()->getPointeeCXXRecordDecl();319 if (Thunk)320 ThisValueClass = Thunk->ThisType->getPointeeCXXRecordDecl();321 322 llvm::Value *AdjustedThisPtr =323 Thunk ? CGM.getCXXABI().performThisAdjustment(*this, LoadCXXThisAddress(),324 ThisValueClass, *Thunk)325 : LoadCXXThis();326 327 // If perfect forwarding is required a variadic method, a method using328 // inalloca, or an unprototyped thunk, use musttail. Emit an error if this329 // thunk requires a return adjustment, since that is impossible with musttail.330 if (CurFnInfo->usesInAlloca() || CurFnInfo->isVariadic() || IsUnprototyped) {331 if (Thunk && !Thunk->Return.isEmpty()) {332 if (IsUnprototyped)333 CGM.ErrorUnsupported(334 MD, "return-adjusting thunk with incomplete parameter type");335 else if (CurFnInfo->isVariadic())336 llvm_unreachable("shouldn't try to emit musttail return-adjusting "337 "thunks for variadic functions");338 else339 CGM.ErrorUnsupported(340 MD, "non-trivial argument copy for return-adjusting thunk");341 }342 EmitMustTailThunk(CurGD, AdjustedThisPtr, Callee);343 return;344 }345 346 // Start building CallArgs.347 CallArgList CallArgs;348 QualType ThisType = MD->getThisType();349 CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);350 351 if (isa<CXXDestructorDecl>(MD))352 CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);353 354#ifndef NDEBUG355 unsigned PrefixArgs = CallArgs.size() - 1;356#endif357 // Add the rest of the arguments.358 for (const ParmVarDecl *PD : MD->parameters())359 EmitDelegateCallArg(CallArgs, PD, SourceLocation());360 361 const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();362 363#ifndef NDEBUG364 const CGFunctionInfo &CallFnInfo = CGM.getTypes().arrangeCXXMethodCall(365 CallArgs, FPT, RequiredArgs::forPrototypePlus(FPT, 1), PrefixArgs);366 assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&367 CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&368 CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());369 assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types370 similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),371 CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));372 assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());373 for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)374 assert(similar(CallFnInfo.arg_begin()[i].info,375 CallFnInfo.arg_begin()[i].type,376 CurFnInfo->arg_begin()[i].info,377 CurFnInfo->arg_begin()[i].type));378#endif379 380 // Determine whether we have a return value slot to use.381 QualType ResultType = CGM.getCXXABI().HasThisReturn(CurGD)382 ? ThisType383 : CGM.getCXXABI().hasMostDerivedReturn(CurGD)384 ? CGM.getContext().VoidPtrTy385 : FPT->getReturnType();386 ReturnValueSlot Slot;387 if (!ResultType->isVoidType() &&388 (CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect ||389 hasAggregateEvaluationKind(ResultType)))390 Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified(),391 /*IsUnused=*/false, /*IsExternallyDestructed=*/true);392 393 // Now emit our call.394 llvm::CallBase *CallOrInvoke;395 RValue RV = EmitCall(*CurFnInfo, CGCallee::forDirect(Callee, CurGD), Slot,396 CallArgs, &CallOrInvoke);397 398 // Consider return adjustment if we have ThunkInfo.399 if (Thunk && !Thunk->Return.isEmpty())400 RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);401 else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(CallOrInvoke))402 Call->setTailCallKind(llvm::CallInst::TCK_Tail);403 404 // Emit return.405 if (!ResultType->isVoidType() && Slot.isNull())406 CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);407 408 // Disable the final ARC autorelease.409 AutoreleaseResult = false;410 411 FinishThunk();412}413 414void CodeGenFunction::EmitMustTailThunk(GlobalDecl GD,415 llvm::Value *AdjustedThisPtr,416 llvm::FunctionCallee Callee) {417 // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery418 // to translate AST arguments into LLVM IR arguments. For thunks, we know419 // that the caller prototype more or less matches the callee prototype with420 // the exception of 'this'.421 SmallVector<llvm::Value *, 8> Args(llvm::make_pointer_range(CurFn->args()));422 423 // Set the adjusted 'this' pointer.424 const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;425 if (ThisAI.isDirect()) {426 const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();427 int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;428 llvm::Type *ThisType = Args[ThisArgNo]->getType();429 if (ThisType != AdjustedThisPtr->getType())430 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);431 Args[ThisArgNo] = AdjustedThisPtr;432 } else {433 assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");434 Address ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);435 llvm::Type *ThisType = ThisAddr.getElementType();436 if (ThisType != AdjustedThisPtr->getType())437 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);438 Builder.CreateStore(AdjustedThisPtr, ThisAddr);439 }440 441 // Emit the musttail call manually. Even if the prologue pushed cleanups, we442 // don't actually want to run them.443 llvm::CallInst *Call = Builder.CreateCall(Callee, Args);444 Call->setTailCallKind(llvm::CallInst::TCK_MustTail);445 446 // Apply the standard set of call attributes.447 unsigned CallingConv;448 llvm::AttributeList Attrs;449 CGM.ConstructAttributeList(Callee.getCallee()->getName(), *CurFnInfo, GD,450 Attrs, CallingConv, /*AttrOnCallSite=*/true,451 /*IsThunk=*/false);452 Call->setAttributes(Attrs);453 Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));454 455 if (Call->getType()->isVoidTy())456 Builder.CreateRetVoid();457 else458 Builder.CreateRet(Call);459 460 // Finish the function to maintain CodeGenFunction invariants.461 // FIXME: Don't emit unreachable code.462 EmitBlock(createBasicBlock());463 464 FinishThunk();465}466 467void CodeGenFunction::generateThunk(llvm::Function *Fn,468 const CGFunctionInfo &FnInfo, GlobalDecl GD,469 const ThunkInfo &Thunk,470 bool IsUnprototyped) {471 StartThunk(Fn, GD, FnInfo, IsUnprototyped);472 // Create a scope with an artificial location for the body of this function.473 auto AL = ApplyDebugLocation::CreateArtificial(*this);474 475 // Get our callee. Use a placeholder type if this method is unprototyped so476 // that CodeGenModule doesn't try to set attributes.477 llvm::Type *Ty;478 if (IsUnprototyped)479 Ty = llvm::StructType::get(getLLVMContext());480 else481 Ty = CGM.getTypes().GetFunctionType(FnInfo);482 483 llvm::Constant *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);484 485 // Make the call and return the result.486 EmitCallAndReturnForThunk(llvm::FunctionCallee(Fn->getFunctionType(), Callee),487 &Thunk, IsUnprototyped);488}489 490static bool shouldEmitVTableThunk(CodeGenModule &CGM, const CXXMethodDecl *MD,491 bool IsUnprototyped, bool ForVTable) {492 // Always emit thunks in the MS C++ ABI. We cannot rely on other TUs to493 // provide thunks for us.494 if (CGM.getTarget().getCXXABI().isMicrosoft())495 return true;496 497 // In the Itanium C++ ABI, vtable thunks are provided by TUs that provide498 // definitions of the main method. Therefore, emitting thunks with the vtable499 // is purely an optimization. Emit the thunk if optimizations are enabled and500 // all of the parameter types are complete.501 if (ForVTable)502 return CGM.getCodeGenOpts().OptimizationLevel && !IsUnprototyped;503 504 // Always emit thunks along with the method definition.505 return true;506}507 508llvm::Constant *CodeGenVTables::maybeEmitThunk(GlobalDecl GD,509 const ThunkInfo &TI,510 bool ForVTable) {511 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());512 513 // First, get a declaration. Compute the mangled name. Don't worry about514 // getting the function prototype right, since we may only need this515 // declaration to fill in a vtable slot.516 SmallString<256> Name;517 MangleContext &MCtx = CGM.getCXXABI().getMangleContext();518 llvm::raw_svector_ostream Out(Name);519 520 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {521 MCtx.mangleCXXDtorThunk(DD, GD.getDtorType(), TI,522 /* elideOverrideInfo */ false, Out);523 } else524 MCtx.mangleThunk(MD, TI, /* elideOverrideInfo */ false, Out);525 526 if (CGM.getContext().useAbbreviatedThunkName(GD, Name.str())) {527 Name = "";528 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))529 MCtx.mangleCXXDtorThunk(DD, GD.getDtorType(), TI,530 /* elideOverrideInfo */ true, Out);531 else532 MCtx.mangleThunk(MD, TI, /* elideOverrideInfo */ true, Out);533 }534 535 llvm::Type *ThunkVTableTy = CGM.getTypes().GetFunctionTypeForVTable(GD);536 llvm::Constant *Thunk = CGM.GetAddrOfThunk(Name, ThunkVTableTy, GD);537 538 // If we don't need to emit a definition, return this declaration as is.539 bool IsUnprototyped = !CGM.getTypes().isFuncTypeConvertible(540 MD->getType()->castAs<FunctionType>());541 if (!shouldEmitVTableThunk(CGM, MD, IsUnprototyped, ForVTable))542 return Thunk;543 544 // Arrange a function prototype appropriate for a function definition. In some545 // cases in the MS ABI, we may need to build an unprototyped musttail thunk.546 const CGFunctionInfo &FnInfo =547 IsUnprototyped ? CGM.getTypes().arrangeUnprototypedMustTailThunk(MD)548 : CGM.getTypes().arrangeGlobalDeclaration(GD);549 llvm::FunctionType *ThunkFnTy = CGM.getTypes().GetFunctionType(FnInfo);550 551 // If the type of the underlying GlobalValue is wrong, we'll have to replace552 // it. It should be a declaration.553 llvm::Function *ThunkFn = cast<llvm::Function>(Thunk->stripPointerCasts());554 if (ThunkFn->getFunctionType() != ThunkFnTy) {555 llvm::GlobalValue *OldThunkFn = ThunkFn;556 557 assert(OldThunkFn->isDeclaration() && "Shouldn't replace non-declaration");558 559 // Remove the name from the old thunk function and get a new thunk.560 OldThunkFn->setName(StringRef());561 ThunkFn = llvm::Function::Create(ThunkFnTy, llvm::Function::ExternalLinkage,562 Name.str(), &CGM.getModule());563 CGM.SetLLVMFunctionAttributes(MD, FnInfo, ThunkFn, /*IsThunk=*/false);564 565 if (!OldThunkFn->use_empty()) {566 OldThunkFn->replaceAllUsesWith(ThunkFn);567 }568 569 // Remove the old thunk.570 OldThunkFn->eraseFromParent();571 }572 573 bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();574 bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;575 576 if (!ThunkFn->isDeclaration()) {577 if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {578 // There is already a thunk emitted for this function, do nothing.579 return ThunkFn;580 }581 582 setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);583 return ThunkFn;584 }585 586 // If this will be unprototyped, add the "thunk" attribute so that LLVM knows587 // that the return type is meaningless. These thunks can be used to call588 // functions with differing return types, and the caller is required to cast589 // the prototype appropriately to extract the correct value.590 if (IsUnprototyped)591 ThunkFn->addFnAttr("thunk");592 593 CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);594 595 // Thunks for variadic methods are special because in general variadic596 // arguments cannot be perfectly forwarded. In the general case, clang597 // implements such thunks by cloning the original function body. However, for598 // thunks with no return adjustment on targets that support musttail, we can599 // use musttail to perfectly forward the variadic arguments.600 bool ShouldCloneVarArgs = false;601 if (!IsUnprototyped && ThunkFn->isVarArg()) {602 ShouldCloneVarArgs = true;603 if (TI.Return.isEmpty()) {604 switch (CGM.getTriple().getArch()) {605 case llvm::Triple::x86_64:606 case llvm::Triple::x86:607 case llvm::Triple::aarch64:608 ShouldCloneVarArgs = false;609 break;610 default:611 break;612 }613 }614 }615 616 if (ShouldCloneVarArgs) {617 if (UseAvailableExternallyLinkage)618 return ThunkFn;619 ThunkFn =620 CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, TI);621 } else {622 // Normal thunk body generation.623 CodeGenFunction(CGM).generateThunk(ThunkFn, FnInfo, GD, TI, IsUnprototyped);624 }625 626 setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);627 return ThunkFn;628}629 630void CodeGenVTables::EmitThunks(GlobalDecl GD) {631 const CXXMethodDecl *MD =632 cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();633 634 // We don't need to generate thunks for the base destructor.635 if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)636 return;637 638 const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =639 VTContext->getThunkInfo(GD);640 641 if (!ThunkInfoVector)642 return;643 644 for (const ThunkInfo& Thunk : *ThunkInfoVector)645 maybeEmitThunk(GD, Thunk, /*ForVTable=*/false);646}647 648void CodeGenVTables::addRelativeComponent(ConstantArrayBuilder &builder,649 llvm::Constant *component,650 unsigned vtableAddressPoint,651 bool vtableHasLocalLinkage,652 bool isCompleteDtor) const {653 // No need to get the offset of a nullptr.654 if (component->isNullValue())655 return builder.add(llvm::ConstantInt::get(CGM.Int32Ty, 0));656 657 auto *globalVal =658 cast<llvm::GlobalValue>(component->stripPointerCastsAndAliases());659 llvm::Module &module = CGM.getModule();660 661 // We don't want to copy the linkage of the vtable exactly because we still662 // want the stub/proxy to be emitted for properly calculating the offset.663 // Examples where there would be no symbol emitted are available_externally664 // and private linkages.665 //666 // `internal` linkage results in STB_LOCAL Elf binding while still manifesting a667 // local symbol.668 //669 // `linkonce_odr` linkage results in a STB_DEFAULT Elf binding but also allows for670 // the rtti_proxy to be transparently replaced with a GOTPCREL reloc by a671 // target that supports this replacement.672 auto stubLinkage = vtableHasLocalLinkage673 ? llvm::GlobalValue::InternalLinkage674 : llvm::GlobalValue::LinkOnceODRLinkage;675 676 llvm::Constant *target;677 if (auto *func = dyn_cast<llvm::Function>(globalVal)) {678 target = llvm::DSOLocalEquivalent::get(func);679 } else {680 llvm::SmallString<16> rttiProxyName(globalVal->getName());681 rttiProxyName.append(".rtti_proxy");682 683 // The RTTI component may not always be emitted in the same linkage unit as684 // the vtable. As a general case, we can make a dso_local proxy to the RTTI685 // that points to the actual RTTI struct somewhere. This will result in a686 // GOTPCREL relocation when taking the relative offset to the proxy.687 llvm::GlobalVariable *proxy = module.getNamedGlobal(rttiProxyName);688 if (!proxy) {689 proxy = new llvm::GlobalVariable(module, globalVal->getType(),690 /*isConstant=*/true, stubLinkage,691 globalVal, rttiProxyName);692 proxy->setDSOLocal(true);693 proxy->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);694 if (!proxy->hasLocalLinkage()) {695 proxy->setVisibility(llvm::GlobalValue::HiddenVisibility);696 proxy->setComdat(module.getOrInsertComdat(rttiProxyName));697 }698 // Do not instrument the rtti proxies with hwasan to avoid a duplicate699 // symbol error. Aliases generated by hwasan will retain the same namebut700 // the addresses they are set to may have different tags from different701 // compilation units. We don't run into this without hwasan because the702 // proxies are in comdat groups, but those aren't propagated to the alias.703 RemoveHwasanMetadata(proxy);704 }705 target = proxy;706 }707 708 builder.addRelativeOffsetToPosition(CGM.Int32Ty, target,709 /*position=*/vtableAddressPoint);710}711 712static bool UseRelativeLayout(const CodeGenModule &CGM) {713 return CGM.getTarget().getCXXABI().isItaniumFamily() &&714 CGM.getItaniumVTableContext().isRelativeLayout();715}716 717bool CodeGenVTables::useRelativeLayout() const {718 return UseRelativeLayout(CGM);719}720 721llvm::Type *CodeGenModule::getVTableComponentType() const {722 if (UseRelativeLayout(*this))723 return Int32Ty;724 return GlobalsInt8PtrTy;725}726 727llvm::Type *CodeGenVTables::getVTableComponentType() const {728 return CGM.getVTableComponentType();729}730 731static void AddPointerLayoutOffset(const CodeGenModule &CGM,732 ConstantArrayBuilder &builder,733 CharUnits offset) {734 builder.add(llvm::ConstantExpr::getIntToPtr(735 llvm::ConstantInt::get(CGM.PtrDiffTy, offset.getQuantity()),736 CGM.GlobalsInt8PtrTy));737}738 739static void AddRelativeLayoutOffset(const CodeGenModule &CGM,740 ConstantArrayBuilder &builder,741 CharUnits offset) {742 builder.add(llvm::ConstantInt::get(CGM.Int32Ty, offset.getQuantity()));743}744 745void CodeGenVTables::addVTableComponent(ConstantArrayBuilder &builder,746 const VTableLayout &layout,747 unsigned componentIndex,748 llvm::Constant *rtti,749 unsigned &nextVTableThunkIndex,750 unsigned vtableAddressPoint,751 bool vtableHasLocalLinkage) {752 auto &component = layout.vtable_components()[componentIndex];753 754 auto addOffsetConstant =755 useRelativeLayout() ? AddRelativeLayoutOffset : AddPointerLayoutOffset;756 757 switch (component.getKind()) {758 case VTableComponent::CK_VCallOffset:759 return addOffsetConstant(CGM, builder, component.getVCallOffset());760 761 case VTableComponent::CK_VBaseOffset:762 return addOffsetConstant(CGM, builder, component.getVBaseOffset());763 764 case VTableComponent::CK_OffsetToTop:765 return addOffsetConstant(CGM, builder, component.getOffsetToTop());766 767 case VTableComponent::CK_RTTI:768 if (useRelativeLayout())769 return addRelativeComponent(builder, rtti, vtableAddressPoint,770 vtableHasLocalLinkage,771 /*isCompleteDtor=*/false);772 else773 return builder.add(rtti);774 775 case VTableComponent::CK_FunctionPointer:776 case VTableComponent::CK_CompleteDtorPointer:777 case VTableComponent::CK_DeletingDtorPointer: {778 GlobalDecl GD = component.getGlobalDecl();779 780 const bool IsThunk =781 nextVTableThunkIndex < layout.vtable_thunks().size() &&782 layout.vtable_thunks()[nextVTableThunkIndex].first == componentIndex;783 784 if (CGM.getLangOpts().CUDA) {785 // Emit NULL for methods we can't codegen on this786 // side. Otherwise we'd end up with vtable with unresolved787 // references.788 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());789 // OK on device side: functions w/ __device__ attribute790 // OK on host side: anything except __device__-only functions.791 bool CanEmitMethod =792 CGM.getLangOpts().CUDAIsDevice793 ? MD->hasAttr<CUDADeviceAttr>()794 : (MD->hasAttr<CUDAHostAttr>() || !MD->hasAttr<CUDADeviceAttr>());795 if (!CanEmitMethod) {796 if (IsThunk)797 nextVTableThunkIndex++;798 return builder.add(799 llvm::ConstantExpr::getNullValue(CGM.GlobalsInt8PtrTy));800 }801 // Method is acceptable, continue processing as usual.802 }803 804 auto getSpecialVirtualFn = [&](StringRef name) -> llvm::Constant * {805 // FIXME(PR43094): When merging comdat groups, lld can select a local806 // symbol as the signature symbol even though it cannot be accessed807 // outside that symbol's TU. The relative vtables ABI would make808 // __cxa_pure_virtual and __cxa_deleted_virtual local symbols, and809 // depending on link order, the comdat groups could resolve to the one810 // with the local symbol. As a temporary solution, fill these components811 // with zero. We shouldn't be calling these in the first place anyway.812 if (useRelativeLayout())813 return llvm::ConstantPointerNull::get(CGM.GlobalsInt8PtrTy);814 815 // For NVPTX devices in OpenMP emit special functon as null pointers,816 // otherwise linking ends up with unresolved references.817 if (CGM.getLangOpts().OpenMP && CGM.getLangOpts().OpenMPIsTargetDevice &&818 CGM.getTriple().isNVPTX())819 return llvm::ConstantPointerNull::get(CGM.GlobalsInt8PtrTy);820 llvm::FunctionType *fnTy =821 llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);822 llvm::Constant *fn = cast<llvm::Constant>(823 CGM.CreateRuntimeFunction(fnTy, name).getCallee());824 if (auto f = dyn_cast<llvm::Function>(fn))825 f->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);826 return fn;827 };828 829 llvm::Constant *fnPtr;830 831 // Pure virtual member functions.832 if (cast<CXXMethodDecl>(GD.getDecl())->isPureVirtual()) {833 if (!PureVirtualFn)834 PureVirtualFn =835 getSpecialVirtualFn(CGM.getCXXABI().GetPureVirtualCallName());836 fnPtr = PureVirtualFn;837 838 // Deleted virtual member functions.839 } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {840 if (!DeletedVirtualFn)841 DeletedVirtualFn =842 getSpecialVirtualFn(CGM.getCXXABI().GetDeletedVirtualCallName());843 fnPtr = DeletedVirtualFn;844 845 // Thunks.846 } else if (IsThunk) {847 auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;848 849 nextVTableThunkIndex++;850 fnPtr = maybeEmitThunk(GD, thunkInfo, /*ForVTable=*/true);851 if (CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers) {852 assert(thunkInfo.Method && "Method not set");853 GD = GD.getWithDecl(thunkInfo.Method);854 }855 856 // Otherwise we can use the method definition directly.857 } else {858 llvm::Type *fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);859 fnPtr = CGM.GetAddrOfFunction(GD, fnTy, /*ForVTable=*/true);860 if (CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers)861 GD = getItaniumVTableContext().findOriginalMethod(GD);862 }863 864 if (useRelativeLayout()) {865 return addRelativeComponent(866 builder, fnPtr, vtableAddressPoint, vtableHasLocalLinkage,867 component.getKind() == VTableComponent::CK_CompleteDtorPointer);868 } else {869 // TODO: this icky and only exists due to functions being in the generic870 // address space, rather than the global one, even though they are871 // globals; fixing said issue might be intrusive, and will be done872 // later.873 unsigned FnAS = fnPtr->getType()->getPointerAddressSpace();874 unsigned GVAS = CGM.GlobalsInt8PtrTy->getPointerAddressSpace();875 876 if (FnAS != GVAS)877 fnPtr =878 llvm::ConstantExpr::getAddrSpaceCast(fnPtr, CGM.GlobalsInt8PtrTy);879 if (const auto &Schema =880 CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers)881 return builder.addSignedPointer(fnPtr, Schema, GD, QualType());882 return builder.add(fnPtr);883 }884 }885 886 case VTableComponent::CK_UnusedFunctionPointer:887 if (useRelativeLayout())888 return builder.add(llvm::ConstantExpr::getNullValue(CGM.Int32Ty));889 else890 return builder.addNullPointer(CGM.GlobalsInt8PtrTy);891 }892 893 llvm_unreachable("Unexpected vtable component kind");894}895 896llvm::Type *CodeGenVTables::getVTableType(const VTableLayout &layout) {897 SmallVector<llvm::Type *, 4> tys;898 llvm::Type *componentType = getVTableComponentType();899 for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i)900 tys.push_back(llvm::ArrayType::get(componentType, layout.getVTableSize(i)));901 902 return llvm::StructType::get(CGM.getLLVMContext(), tys);903}904 905void CodeGenVTables::createVTableInitializer(ConstantStructBuilder &builder,906 const VTableLayout &layout,907 llvm::Constant *rtti,908 bool vtableHasLocalLinkage) {909 llvm::Type *componentType = getVTableComponentType();910 911 const auto &addressPoints = layout.getAddressPointIndices();912 unsigned nextVTableThunkIndex = 0;913 for (unsigned vtableIndex = 0, endIndex = layout.getNumVTables();914 vtableIndex != endIndex; ++vtableIndex) {915 auto vtableElem = builder.beginArray(componentType);916 917 size_t vtableStart = layout.getVTableOffset(vtableIndex);918 size_t vtableEnd = vtableStart + layout.getVTableSize(vtableIndex);919 for (size_t componentIndex = vtableStart; componentIndex < vtableEnd;920 ++componentIndex) {921 addVTableComponent(vtableElem, layout, componentIndex, rtti,922 nextVTableThunkIndex, addressPoints[vtableIndex],923 vtableHasLocalLinkage);924 }925 vtableElem.finishAndAddTo(builder);926 }927}928 929llvm::GlobalVariable *CodeGenVTables::GenerateConstructionVTable(930 const CXXRecordDecl *RD, const BaseSubobject &Base, bool BaseIsVirtual,931 llvm::GlobalVariable::LinkageTypes Linkage,932 VTableAddressPointsMapTy &AddressPoints) {933 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())934 DI->completeClassData(Base.getBase());935 936 std::unique_ptr<VTableLayout> VTLayout(937 getItaniumVTableContext().createConstructionVTableLayout(938 Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));939 940 // Add the address points.941 AddressPoints = VTLayout->getAddressPoints();942 943 // Get the mangled construction vtable name.944 SmallString<256> OutName;945 llvm::raw_svector_ostream Out(OutName);946 cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())947 .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),948 Base.getBase(), Out);949 SmallString<256> Name(OutName);950 951 bool UsingRelativeLayout = getItaniumVTableContext().isRelativeLayout();952 bool VTableAliasExists =953 UsingRelativeLayout && CGM.getModule().getNamedAlias(Name);954 if (VTableAliasExists) {955 // We previously made the vtable hidden and changed its name.956 Name.append(".local");957 }958 959 llvm::Type *VTType = getVTableType(*VTLayout);960 961 // Construction vtable symbols are not part of the Itanium ABI, so we cannot962 // guarantee that they actually will be available externally. Instead, when963 // emitting an available_externally VTT, we provide references to an internal964 // linkage construction vtable. The ABI only requires complete-object vtables965 // to be the same for all instances of a type, not construction vtables.966 if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)967 Linkage = llvm::GlobalVariable::InternalLinkage;968 969 llvm::Align Align = CGM.getDataLayout().getABITypeAlign(VTType);970 971 // Create the variable that will hold the construction vtable.972 llvm::GlobalVariable *VTable =973 CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage, Align);974 975 // V-tables are always unnamed_addr.976 VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);977 978 llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(979 CGM.getContext().getCanonicalTagType(Base.getBase()));980 981 // Create and set the initializer.982 ConstantInitBuilder builder(CGM);983 auto components = builder.beginStruct();984 createVTableInitializer(components, *VTLayout, RTTI,985 VTable->hasLocalLinkage());986 components.finishAndSetAsInitializer(VTable);987 988 // Set properties only after the initializer has been set to ensure that the989 // GV is treated as definition and not declaration.990 assert(!VTable->isDeclaration() && "Shouldn't set properties on declaration");991 CGM.setGVProperties(VTable, RD);992 993 CGM.EmitVTableTypeMetadata(RD, VTable, *VTLayout);994 995 if (UsingRelativeLayout) {996 RemoveHwasanMetadata(VTable);997 if (!VTable->isDSOLocal())998 GenerateRelativeVTableAlias(VTable, OutName);999 }1000 1001 return VTable;1002}1003 1004// Ensure this vtable is not instrumented by hwasan. That is, a global alias is1005// not generated for it. This is mainly used by the relative-vtables ABI where1006// vtables instead contain 32-bit offsets between the vtable and function1007// pointers. Hwasan is disabled for these vtables for now because the tag in a1008// vtable pointer may fail the overflow check when resolving 32-bit PLT1009// relocations. A future alternative for this would be finding which usages of1010// the vtable can continue to use the untagged hwasan value without any loss of1011// value in hwasan.1012void CodeGenVTables::RemoveHwasanMetadata(llvm::GlobalValue *GV) const {1013 if (CGM.getLangOpts().Sanitize.has(SanitizerKind::HWAddress)) {1014 llvm::GlobalValue::SanitizerMetadata Meta;1015 if (GV->hasSanitizerMetadata())1016 Meta = GV->getSanitizerMetadata();1017 Meta.NoHWAddress = true;1018 GV->setSanitizerMetadata(Meta);1019 }1020}1021 1022// If the VTable is not dso_local, then we will not be able to indicate that1023// the VTable does not need a relocation and move into rodata. A frequent1024// time this can occur is for classes that should be made public from a DSO1025// (like in libc++). For cases like these, we can make the vtable hidden or1026// internal and create a public alias with the same visibility and linkage as1027// the original vtable type.1028void CodeGenVTables::GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,1029 llvm::StringRef AliasNameRef) {1030 assert(getItaniumVTableContext().isRelativeLayout() &&1031 "Can only use this if the relative vtable ABI is used");1032 assert(!VTable->isDSOLocal() && "This should be called only if the vtable is "1033 "not guaranteed to be dso_local");1034 1035 // If the vtable is available_externally, we shouldn't (or need to) generate1036 // an alias for it in the first place since the vtable won't actually by1037 // emitted in this compilation unit.1038 if (VTable->hasAvailableExternallyLinkage())1039 return;1040 1041 // Create a new string in the event the alias is already the name of the1042 // vtable. Using the reference directly could lead to use of an inititialized1043 // value in the module's StringMap.1044 llvm::SmallString<256> AliasName(AliasNameRef);1045 VTable->setName(AliasName + ".local");1046 1047 auto Linkage = VTable->getLinkage();1048 assert(llvm::GlobalAlias::isValidLinkage(Linkage) &&1049 "Invalid vtable alias linkage");1050 1051 llvm::GlobalAlias *VTableAlias = CGM.getModule().getNamedAlias(AliasName);1052 if (!VTableAlias) {1053 VTableAlias = llvm::GlobalAlias::create(VTable->getValueType(),1054 VTable->getAddressSpace(), Linkage,1055 AliasName, &CGM.getModule());1056 } else {1057 assert(VTableAlias->getValueType() == VTable->getValueType());1058 assert(VTableAlias->getLinkage() == Linkage);1059 }1060 VTableAlias->setVisibility(VTable->getVisibility());1061 VTableAlias->setUnnamedAddr(VTable->getUnnamedAddr());1062 1063 // Both of these will now imply dso_local for the vtable.1064 if (!VTable->hasComdat()) {1065 VTable->setLinkage(llvm::GlobalValue::InternalLinkage);1066 } else {1067 // If a relocation targets an internal linkage symbol, MC will generate the1068 // relocation against the symbol's section instead of the symbol itself1069 // (see ELFObjectWriter::shouldRelocateWithSymbol). If an internal symbol is1070 // in a COMDAT section group, that section might be discarded, and then the1071 // relocation to that section will generate a linker error. We therefore1072 // make COMDAT vtables hidden instead of internal: they'll still not be1073 // public, but relocations will reference the symbol instead of the section1074 // and COMDAT deduplication will thus work as expected.1075 VTable->setVisibility(llvm::GlobalValue::HiddenVisibility);1076 }1077 1078 VTableAlias->setAliasee(VTable);1079}1080 1081static bool shouldEmitAvailableExternallyVTable(const CodeGenModule &CGM,1082 const CXXRecordDecl *RD) {1083 return CGM.getCodeGenOpts().OptimizationLevel > 0 &&1084 CGM.getCXXABI().canSpeculativelyEmitVTable(RD);1085}1086 1087/// Compute the required linkage of the vtable for the given class.1088///1089/// Note that we only call this at the end of the translation unit.1090llvm::GlobalVariable::LinkageTypes1091CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {1092 if (!RD->isExternallyVisible())1093 return llvm::GlobalVariable::InternalLinkage;1094 1095 // In windows, the linkage of vtable is not related to modules.1096 bool IsInNamedModule = !getTarget().getCXXABI().isMicrosoft() &&1097 RD->isInNamedModule();1098 // If the CXXRecordDecl is not in a module unit, we need to get1099 // its key function. We're at the end of the translation unit, so the current1100 // key function is fully correct.1101 const CXXMethodDecl *keyFunction =1102 IsInNamedModule ? nullptr : Context.getCurrentKeyFunction(RD);1103 if (IsInNamedModule || (keyFunction && !RD->hasAttr<DLLImportAttr>())) {1104 // If this class has a key function, use that to determine the1105 // linkage of the vtable.1106 const FunctionDecl *def = nullptr;1107 if (keyFunction && keyFunction->hasBody(def))1108 keyFunction = cast<CXXMethodDecl>(def);1109 1110 bool IsExternalDefinition =1111 IsInNamedModule ? RD->shouldEmitInExternalSource() : !def;1112 1113 TemplateSpecializationKind Kind =1114 IsInNamedModule ? RD->getTemplateSpecializationKind()1115 : keyFunction->getTemplateSpecializationKind();1116 1117 switch (Kind) {1118 case TSK_Undeclared:1119 case TSK_ExplicitSpecialization:1120 assert(1121 (IsInNamedModule || def || CodeGenOpts.OptimizationLevel > 0 ||1122 CodeGenOpts.getDebugInfo() != llvm::codegenoptions::NoDebugInfo) &&1123 "Shouldn't query vtable linkage without the class in module units, "1124 "key function, optimizations, or debug info");1125 if (IsExternalDefinition && CodeGenOpts.OptimizationLevel > 0)1126 return llvm::GlobalVariable::AvailableExternallyLinkage;1127 1128 if (keyFunction && keyFunction->isInlined())1129 return !Context.getLangOpts().AppleKext1130 ? llvm::GlobalVariable::LinkOnceODRLinkage1131 : llvm::Function::InternalLinkage;1132 1133 return llvm::GlobalVariable::ExternalLinkage;1134 1135 case TSK_ImplicitInstantiation:1136 return !Context.getLangOpts().AppleKext ?1137 llvm::GlobalVariable::LinkOnceODRLinkage :1138 llvm::Function::InternalLinkage;1139 1140 case TSK_ExplicitInstantiationDefinition:1141 return !Context.getLangOpts().AppleKext ?1142 llvm::GlobalVariable::WeakODRLinkage :1143 llvm::Function::InternalLinkage;1144 1145 case TSK_ExplicitInstantiationDeclaration:1146 return IsExternalDefinition1147 ? llvm::GlobalVariable::AvailableExternallyLinkage1148 : llvm::GlobalVariable::ExternalLinkage;1149 }1150 }1151 1152 // -fapple-kext mode does not support weak linkage, so we must use1153 // internal linkage.1154 if (Context.getLangOpts().AppleKext)1155 return llvm::Function::InternalLinkage;1156 1157 llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =1158 llvm::GlobalValue::LinkOnceODRLinkage;1159 llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =1160 llvm::GlobalValue::WeakODRLinkage;1161 if (RD->hasAttr<DLLExportAttr>()) {1162 // Cannot discard exported vtables.1163 DiscardableODRLinkage = NonDiscardableODRLinkage;1164 } else if (RD->hasAttr<DLLImportAttr>()) {1165 // Imported vtables are available externally.1166 DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;1167 NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;1168 }1169 1170 switch (RD->getTemplateSpecializationKind()) {1171 case TSK_Undeclared:1172 case TSK_ExplicitSpecialization:1173 case TSK_ImplicitInstantiation:1174 return DiscardableODRLinkage;1175 1176 case TSK_ExplicitInstantiationDeclaration:1177 // Explicit instantiations in MSVC do not provide vtables, so we must emit1178 // our own.1179 if (getTarget().getCXXABI().isMicrosoft())1180 return DiscardableODRLinkage;1181 return shouldEmitAvailableExternallyVTable(*this, RD)1182 ? llvm::GlobalVariable::AvailableExternallyLinkage1183 : llvm::GlobalVariable::ExternalLinkage;1184 1185 case TSK_ExplicitInstantiationDefinition:1186 return NonDiscardableODRLinkage;1187 }1188 1189 llvm_unreachable("Invalid TemplateSpecializationKind!");1190}1191 1192/// This is a callback from Sema to tell us that a particular vtable is1193/// required to be emitted in this translation unit.1194///1195/// This is only called for vtables that _must_ be emitted (mainly due to key1196/// functions). For weak vtables, CodeGen tracks when they are needed and1197/// emits them as-needed.1198void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {1199 VTables.GenerateClassData(theClass);1200}1201 1202void1203CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {1204 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())1205 DI->completeClassData(RD);1206 1207 if (RD->getNumVBases())1208 CGM.getCXXABI().emitVirtualInheritanceTables(RD);1209 1210 CGM.getCXXABI().emitVTableDefinitions(*this, RD);1211}1212 1213/// At this point in the translation unit, does it appear that can we1214/// rely on the vtable being defined elsewhere in the program?1215///1216/// The response is really only definitive when called at the end of1217/// the translation unit.1218///1219/// The only semantic restriction here is that the object file should1220/// not contain a vtable definition when that vtable is defined1221/// strongly elsewhere. Otherwise, we'd just like to avoid emitting1222/// vtables when unnecessary.1223bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {1224 assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");1225 1226 // We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't1227 // emit them even if there is an explicit template instantiation.1228 if (CGM.getTarget().getCXXABI().isMicrosoft())1229 return false;1230 1231 // If we have an explicit instantiation declaration (and not a1232 // definition), the vtable is defined elsewhere.1233 TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();1234 if (TSK == TSK_ExplicitInstantiationDeclaration)1235 return true;1236 1237 // Otherwise, if the class is an instantiated template, the1238 // vtable must be defined here.1239 if (TSK == TSK_ImplicitInstantiation ||1240 TSK == TSK_ExplicitInstantiationDefinition)1241 return false;1242 1243 // Otherwise, if the class is attached to a module, the tables are uniquely1244 // emitted in the object for the module unit in which it is defined.1245 if (RD->isInNamedModule())1246 return RD->shouldEmitInExternalSource();1247 1248 // Otherwise, if the class doesn't have a key function (possibly1249 // anymore), the vtable must be defined here.1250 const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);1251 if (!keyFunction)1252 return false;1253 1254 // Otherwise, if we don't have a definition of the key function, the1255 // vtable must be defined somewhere else.1256 return !keyFunction->hasBody();1257}1258 1259/// Given that we're currently at the end of the translation unit, and1260/// we've emitted a reference to the vtable for this class, should1261/// we define that vtable?1262static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,1263 const CXXRecordDecl *RD) {1264 // If vtable is internal then it has to be done.1265 if (!CGM.getVTables().isVTableExternal(RD))1266 return true;1267 1268 // If it's external then maybe we will need it as available_externally.1269 return shouldEmitAvailableExternallyVTable(CGM, RD);1270}1271 1272/// Given that at some point we emitted a reference to one or more1273/// vtables, and that we are now at the end of the translation unit,1274/// decide whether we should emit them.1275void CodeGenModule::EmitDeferredVTables() {1276#ifndef NDEBUG1277 // Remember the size of DeferredVTables, because we're going to assume1278 // that this entire operation doesn't modify it.1279 size_t savedSize = DeferredVTables.size();1280#endif1281 1282 for (const CXXRecordDecl *RD : DeferredVTables)1283 if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))1284 VTables.GenerateClassData(RD);1285 else if (shouldOpportunisticallyEmitVTables())1286 OpportunisticVTables.push_back(RD);1287 1288 assert(savedSize == DeferredVTables.size() &&1289 "deferred extra vtables during vtable emission?");1290 DeferredVTables.clear();1291}1292 1293bool CodeGenModule::AlwaysHasLTOVisibilityPublic(const CXXRecordDecl *RD) {1294 if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>() ||1295 RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())1296 return true;1297 1298 if (!getCodeGenOpts().LTOVisibilityPublicStd)1299 return false;1300 1301 const DeclContext *DC = RD;1302 while (true) {1303 auto *D = cast<Decl>(DC);1304 DC = DC->getParent();1305 if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {1306 if (auto *ND = dyn_cast<NamespaceDecl>(D))1307 if (const IdentifierInfo *II = ND->getIdentifier())1308 if (II->isStr("std") || II->isStr("stdext"))1309 return true;1310 break;1311 }1312 }1313 1314 return false;1315}1316 1317bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {1318 LinkageInfo LV = RD->getLinkageAndVisibility();1319 if (!isExternallyVisible(LV.getLinkage()))1320 return true;1321 1322 if (!getTriple().isOSBinFormatCOFF() &&1323 LV.getVisibility() != HiddenVisibility)1324 return false;1325 1326 return !AlwaysHasLTOVisibilityPublic(RD);1327}1328 1329llvm::GlobalObject::VCallVisibility CodeGenModule::GetVCallVisibilityLevel(1330 const CXXRecordDecl *RD, llvm::DenseSet<const CXXRecordDecl *> &Visited) {1331 // If we have already visited this RD (which means this is a recursive call1332 // since the initial call should have an empty Visited set), return the max1333 // visibility. The recursive calls below compute the min between the result1334 // of the recursive call and the current TypeVis, so returning the max here1335 // ensures that it will have no effect on the current TypeVis.1336 if (!Visited.insert(RD).second)1337 return llvm::GlobalObject::VCallVisibilityTranslationUnit;1338 1339 LinkageInfo LV = RD->getLinkageAndVisibility();1340 llvm::GlobalObject::VCallVisibility TypeVis;1341 if (!isExternallyVisible(LV.getLinkage()))1342 TypeVis = llvm::GlobalObject::VCallVisibilityTranslationUnit;1343 else if (HasHiddenLTOVisibility(RD))1344 TypeVis = llvm::GlobalObject::VCallVisibilityLinkageUnit;1345 else1346 TypeVis = llvm::GlobalObject::VCallVisibilityPublic;1347 1348 for (const auto &B : RD->bases())1349 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())1350 TypeVis = std::min(1351 TypeVis,1352 GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));1353 1354 for (const auto &B : RD->vbases())1355 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())1356 TypeVis = std::min(1357 TypeVis,1358 GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));1359 1360 return TypeVis;1361}1362 1363void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,1364 llvm::GlobalVariable *VTable,1365 const VTableLayout &VTLayout) {1366 // Emit type metadata on vtables with LTO or IR instrumentation.1367 // In IR instrumentation, the type metadata is used to find out vtable1368 // definitions (for type profiling) among all global variables.1369 if (!getCodeGenOpts().LTOUnit && !getCodeGenOpts().hasProfileIRInstr())1370 return;1371 1372 CharUnits ComponentWidth = GetTargetTypeStoreSize(getVTableComponentType());1373 1374 struct AddressPoint {1375 const CXXRecordDecl *Base;1376 size_t Offset;1377 std::string TypeName;1378 bool operator<(const AddressPoint &RHS) const {1379 int D = TypeName.compare(RHS.TypeName);1380 return D < 0 || (D == 0 && Offset < RHS.Offset);1381 }1382 };1383 std::vector<AddressPoint> AddressPoints;1384 for (auto &&AP : VTLayout.getAddressPoints()) {1385 AddressPoint N{AP.first.getBase(),1386 VTLayout.getVTableOffset(AP.second.VTableIndex) +1387 AP.second.AddressPointIndex,1388 {}};1389 llvm::raw_string_ostream Stream(N.TypeName);1390 CanQualType T = getContext().getCanonicalTagType(N.Base);1391 getCXXABI().getMangleContext().mangleCanonicalTypeName(T, Stream);1392 AddressPoints.push_back(std::move(N));1393 }1394 1395 // Sort the address points for determinism.1396 llvm::sort(AddressPoints);1397 1398 ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();1399 for (auto AP : AddressPoints) {1400 // Create type metadata for the address point.1401 AddVTableTypeMetadata(VTable, ComponentWidth * AP.Offset, AP.Base);1402 1403 // The class associated with each address point could also potentially be1404 // used for indirect calls via a member function pointer, so we need to1405 // annotate the address of each function pointer with the appropriate member1406 // function pointer type.1407 for (unsigned I = 0; I != Comps.size(); ++I) {1408 if (Comps[I].getKind() != VTableComponent::CK_FunctionPointer)1409 continue;1410 llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(1411 Context.getMemberPointerType(Comps[I].getFunctionDecl()->getType(),1412 /*Qualifier=*/std::nullopt, AP.Base));1413 VTable->addTypeMetadata((ComponentWidth * I).getQuantity(), MD);1414 }1415 }1416 1417 if (getCodeGenOpts().VirtualFunctionElimination ||1418 getCodeGenOpts().WholeProgramVTables) {1419 llvm::DenseSet<const CXXRecordDecl *> Visited;1420 llvm::GlobalObject::VCallVisibility TypeVis =1421 GetVCallVisibilityLevel(RD, Visited);1422 if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)1423 VTable->setVCallVisibilityMetadata(TypeVis);1424 }1425}1426